Conductive Feature Formation

ABSTRACT

The present disclosure provides example embodiments relating to conductive features, and methods of forming the conductive features, that have differing dimensions. In an embodiment, a structure includes a substrate, a dielectric layer over the substrate, and first and second conductive features through the dielectric layer to first and second source/drain regions, respectively, on the substrate. The first conductive feature has a first length along a longitudinal axis of the first conductive feature and a first width perpendicular to the first length. The second conductive feature has a second length along a longitudinal axis of the second conductive feature and a second width perpendicular to the second length. The longitudinal axis of the first conductive feature is aligned with the longitudinal axis of the second conductive feature. The first width is greater than the second width, and the first length is less than the second length.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.17/062,848, filed on Oct. 5, 2020, entitled “Conductive FeatureFormation,” which is a divisional of U.S. patent application Ser. No.16/145,432, filed on Sep. 28, 2018, entitled “Conductive FeatureFormation,” now U.S. Pat. No. 10,797,058 issued Oct. 6, 2020, eachapplication is hereby incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (e.g., the number of interconnecteddevices per chip area) has generally increased while geometry size(e.g., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. However, scaling down has also led to challenges thatmay not have been presented by previous generations at largergeometries.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a circuit schematic of a static random access memory (SRAM)cell in accordance with some embodiments.

FIG. 2 is a layout of four SRAM cells in accordance with someembodiments.

FIGS. 3A, 3B, 3C, 4A, 4B, 4C, 5A, 5B, 5C, 6A, 6B, 6C, 7A, 7B, 7C, 8A,8B, 8C, 9A, 9B, 9C, 10A, 10B, and 10C are views of respectiveintermediate structures at respective stages during an example processfor forming an SRAM structure in accordance with some embodiments.

FIGS. 11A, 11B, 11C, 12A, 12B, 12C, 13A, 13B, 13C, 14A, 14B, 14C, 15A,15B, 15C, 16A, 16B, and 16C are views of respective intermediatestructures at respective stages during another example process forforming an SRAM structure in accordance with some embodiments.

FIG. 17 is a graph illustrating pulsing of power of a plasma generatorand a bias voltage of a substrate holder during an opening-widening etchprocess in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure provides some example embodiments relating toconductive features, and methods of forming the conductive features,that have differing dimensions. In some applications, conductivefeatures having differing lateral dimensions may be implemented. Withthe downscaling of feature sizes, filling of conductive features with aconductive material may become more challenging. In examples describedherein, some conductive features that have a smaller length than otherconductive features can be formed with a larger width than the otherconductive features. By increasing the width of these conductivefeatures that have a smaller length, gap fill by the conductive materialthat forms the conductive features can be improved. Further, the widthof the conductive features that have larger lengths may be reduced,which can increase a processing window between those conductive featuresand proximate gate structures. Other benefits can be achieved.

Example embodiments described herein are described in the context offorming conductive features to source/drain regions in a static randomaccess memory (SRAM) structure. Other embodiments may be implemented inother contexts, such as where other conductive features may be formedwith different sizes in Front End Of the Line (FEOL) processing, MiddleEnd Of the Line (MEOL) processing, and Back End Of the Line (BEOL)processing. Example embodiments may have broad applicability to formopening sizes for conductive features. Some variations of the examplemethods and structures are described. A person having ordinary skill inthe art will readily understand other modifications that may be madethat are contemplated within the scope of other embodiments. Althoughmethod embodiments may be described in a particular order, various othermethod embodiments may be performed in any logical order and may includefewer or more steps than what is described herein. In some figures, somereference numbers of components or features illustrated therein may beomitted to avoid obscuring other components or features; this is forease of depicting the figures.

FIG. 1 illustrates a circuit schematic of a static random access memory(SRAM) cell 100. The SRAM cell 100 includes first and second pass-gatetransistors PG1 and PG2, first and second pull-up transistors PU1 andPU2, and first and second pull-down transistors PD1 and PD2. A firstsource/drain of the first pass-gate transistor PG1 is electricallycoupled to a bit line node BL, and a second source/drain of the firstpass-gate transistor PG1 is electrically coupled to a first intra-cellnode nN1. The gate of the first pass-gate transistor PG1 is electricallycoupled to a word line node WL. A first source/drain of the secondpass-gate transistor PG2 is electrically coupled to a complementary bitline node BLB, and a second source/drain of the second pass-gatetransistor PG2 is electrically coupled to a second intra-cell node nN2.The gate of the second pass-gate transistor PG2 is electrically coupledto a word line node WL.

The first pull-up and pull-down transistors PU1 and PD1 and the secondpull-up and pull-down transistors PU2 and PD2 form cross-coupledinverters to form a memory element. The sources of the first and secondpull-up transistors PU1 and PU2 are electrically coupled to a firstpower node VDD, and sources of the first and second pull-downtransistors PD1 and PD2 are electrically coupled to a second power nodeVSS (e.g., ground). The drains of the first pull-up and pull-downtransistors PU1 and PD1 are electrically coupled together and to thefirst intra-cell node nN1, which is further electrically coupled to thegates of the second pull-up and pull-down transistors PU2 and PD2. Thedrains of the second pull-up and pull-down transistors PU2 and PD2 areelectrically coupled together and to the second intra-cell node nN2,which is further electrically coupled to the gates of the first pull-upand pull-down transistors PU1 and PD1. As illustrated in FIG. 1, thepass-gate transistors PG1 and PG2 and the pull-down transistors PD1 andPD2 are n-type field effect transistors (nFETs), and the pull-uptransistors PU1 and PU2 are p-type FETs (pFETs). A person havingordinary skill in the art will readily understand the operation of theSRAM cell 100.

FIG. 2 illustrates a layout of four SRAM cells 100 a, 100 b, 100 c, and100 d (each implementing the SRAM cell 100 of FIG. 1) in accordance withsome embodiments. The SRAM cell 100 a includes fins 22 on asemiconductor substrate 20 (to be described subsequently). The fins 22form the active areas of the transistors of the SRAM cell 100 a. Asillustrated, two fins 22 form each active area of a respectivetransistor, although in other examples, one, three, or more fins canform an active area of a transistor. Further, each transistor of theSRAM cell 100 a can include any number of fins as the active area, whichmay be the same or different from other transistors within the SRAM cell100 a. The SRAM cell 100 a further includes gate structures 47. Thevarious fins 22 and gate structures 47 together form the transistorsdescribed in the SRAM cell 100 in FIG. 1. The layout of the SRAM cell100 a is mirrored along an interface between the SRAM cell 100 a and theSRAM cell 100 b to form the layout of the SRAM cell 100 b. Similarly,the layout of the SRAM cell 100 a is mirrored along an interface betweenthe SRAM cell 100 a and the SRAM cell 100 c to form the layout of theSRAM cell 100 c. The layout of the SRAM cell 100 c is mirrored along aninterface between the SRAM cell 100 c and the SRAM cell 100 d to formthe layout of the SRAM cell 100 d. A person having ordinary skill in theart will readily understand various features and aspects of this layoutthat are not explicitly described herein. Some features of this layoutare described below in the context of other figures. The layout of thefour SRAM cells in FIG. 2 can be repeated any number of times toimplement an SRAM array having any size.

FIG. 2 further illustrates a cross-section X-X along the interfacebetween the SRAM cells 100 a and 100 c, and illustrates a cross-sectionY-Y that is perpendicular to the cross-section X-X and is along a fin 22that forms the first pass gate transistors PG1 in the SRAM cells 100 aand 100 c. Subsequent figures with an “A” designation illustrate layoutsof intermediate structures at various stages of fabrication thatcorrespond to the layout of FIG. 2. Subsequent figures with a “B”designation illustrate cross-sectional views of the intermediatestructures at various stages of fabrication that correspond tocross-section X-X in FIG. 2. Subsequent figures with a “C” designationillustrate cross-sectional views of the intermediate structures atvarious stages of fabrication that correspond to cross-section Y-Y inFIG. 2.

FIGS. 3A-3C through 10A-10C illustrate views of respective intermediatestructures at respective stages during an example process for forming anSRAM structure in accordance with some embodiments.

FIGS. 3A, 3B, and 3C illustrate the formation of a tri-layer mask overFinFET structures that are formed. The formation of the FinFETstructures is according to the layout of FIG. 2 and is described brieflybelow.

Referring to FIGS. 3B and 3C, fins 22 are formed on a semiconductorsubstrate 20. The semiconductor substrate 20 may be or include a bulksemiconductor substrate, a semiconductor-on-insulator (SOI) substrate,or the like, which may be doped (e.g., with a p-type or an n-typedopant) or undoped. In some embodiments, the semiconductor material ofthe semiconductor substrate 20 may include an elemental semiconductorsuch as silicon (Si) or germanium (Ge); a compound semiconductorincluding; an alloy semiconductor; or a combination thereof.

The fins 22 are formed on the semiconductor substrate 20, such as byetching trenches in the semiconductor substrate 20 to form the fins 22(which include a semiconductor material of the semiconductor substrate20). The fins 22 may be patterned in the semiconductor substrate 20 byany suitable method. For example, the fins 22 may be patterned using oneor more photolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in some embodiments, asacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins 22.

Isolation structures 24 are formed with each being in a correspondingtrench. The isolation structures 24 may include or be an insulatingmaterial such as an oxide (such as silicon oxide), a nitride, the like,or a combination thereof, and the insulating material may be depositedusing an appropriate deposition process. The insulating material may berecessed after being deposited to form the isolation structures 24. Theinsulating material is recessed such that the fins 22 protrude frombetween neighboring isolation structures 24, which may, at least inpart, thereby delineate the fins 22 as active areas on the semiconductorsubstrate 20. A person having ordinary skill in the art will readilyunderstand that the processes described above are just examples of howfins 22 may be formed. In other examples, the fins 22 may be formed byother processes and may include heteroepitaxial and/or homoepitaxialstructures.

Dummy gate stacks (or more generally, gate structures) (not illustrated)are formed across the fins 22 and isolation structures 24. The dummygate stacks are formed where the gate structures 47 illustrated in FIG.3C are formed, as will become apparent. The dummy gate stacks extendlongitudinally perpendicularly to respective longitudinal directions ofthe fins 22. Each dummy gate stack can include an interfacial dielectricalong and on the fins 22, a dummy gate over the interfacial dielectric,and a mask over the dummy gate.

The interfacial dielectrics may include or be silicon oxide, siliconnitride, the like, or multilayers thereof. The dummy gates may includeor be silicon (e.g., amorphous silicon or polysilicon) or anothermaterial. The masks may include or be silicon nitride, siliconoxynitride, silicon carbon nitride, the like, or a combination thereof.Layers for the interfacial dielectrics, dummy gates, and masks for thedummy gate stacks may be sequentially deposited or formed, such as byany acceptable deposition technique, and then patterned, for example,using photolithography and one or more etch processes, into the dummygate stacks.

Gate spacers 26 are formed along sidewalls of the dummy gate stacks andover the fins 22. The gate spacers 26 may be formed by conformallydepositing one or more layers for the gate spacers 26 andanisotropically etching the one or more layers, for example, byappropriate processes. The one or more layers for the gate spacers 26may include or be silicon nitride, silicon oxynitride, silicon carbonnitride, the like, multi-layers thereof, or a combination thereof.

Recesses are then formed in the fins 22 on opposing sides of the dummygate stacks. The recessing can be by an etch process. The etch processcan be isotropic or anisotropic, or further, may be selective withrespect to one or more crystalline planes of the semiconductor substrate20. Hence, the recesses can have various cross-sectional profiles basedon the etch process implemented.

Epitaxial source/drain structures 28 are formed in the recesses. Theepitaxial source/drain structures 28 for different conductivity typeFinFET structures can be formed of different materials, for example. Insuch examples, appropriate masking can be performed to mask one regionwhile forming epitaxial source/drain structures 28 in another region.Regions with n-type FinFET structures (such as regions that include thepass-gate transistors PG1 and PG2 and the pull-down transistors PD1 andPD2) can be masked while epitaxial source/drain structures 28 areepitaxially grown in recesses in fins 22 of p-type FinFET structures(such as in regions that include the pull-up transistors PU1 and PU2).Conversely, regions p-type FinFET structures can be masked whileepitaxial source/drain structures 28 are epitaxially grown in recessesin fins 22 of n-type FinFET structures.

The epitaxial source/drain structures 28 may include or be silicongermanium, germanium, silicon carbide, silicon phosphorus, siliconcarbon phosphorus, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like. A person having ordinary skill in the artwill readily understand materials that can be implemented for n-typeFinFET structures and for p-type FinFET structures.

The epitaxial source/drain structures 28 may be formed in the recessesby epitaxial growth with appropriate deposition processes. In someexamples, some epitaxial source/drain structures 28 may be formed withfacets (which may correspond to crystalline planes of the semiconductorsubstrate 20), such as shown in FIG. 3B. In some examples, someepitaxial source/drain structures 28 may be formed with differentcross-sectional profiles, such as also shown in FIG. 3B, which may be aresult of different materials being epitaxially grown and/or growing thematerials under different process conditions. Further, the epitaxialsource/drain structures 28 may be formed at a raised height with respectto the respective fin 22, such as shown in FIG. 3C. In some examples,epitaxial source/drain structures 28 in some fins 22 can be epitaxiallygrown to merge together, such as due to proximity to neighboring fins22.

In some examples, the epitaxial source/drain structures 28 may also bedoped, such as by in situ doping during epitaxial growth and/or byimplanting dopants into the epitaxial source/drain structures 28 afterepitaxial growth. Hence, a source/drain region may be delineated bydoping (e.g., by in situ doping during epitaxial growth) and/or byepitaxial growth, which may further delineate the active area in whichthe source/drain region is delineated.

A contact etch stop layer (CESL) 30 is conformally deposited on surfacesof the epitaxial source/drain structures 28, sidewalls and top surfacesof the gate spacers 26, top surfaces of the masks, and top surfaces ofthe isolation structures 24. An etch stop layer can provide a mechanismto stop an etch process when forming, e.g., contacts or vias by having adifferent etch selectivity from adjacent layers or components. The CESL30 may comprise or be silicon nitride, silicon carbon nitride, carbonnitride, the like, or a combination thereof, and may be deposited by anyappropriate conformal deposition process.

A first interlayer dielectric (ILD) 32 is formed over the CESL 30. Thefirst ILD 32 may comprise or be silicon dioxide, a low-k dielectricmaterial (e.g., a material having a dielectric constant lower thansilicon dioxide), silicon oxynitride, phosphosilicate glass (PSG),borosilicate glass (BSG), borophosphosilicate glass (BPSG), undopedsilicate glass (USG), fluorinated silicate glass (FSG), organosilicateglasses (OSG), SiO_(x)C_(y), silicon carbon material, a compoundthereof, a composite thereof, the like, or a combination thereof. Thefirst ILD 32 may be deposited by any acceptable deposition process.

The first ILD 32 and CESL 30 are formed with top surfaces coplanar withtop surfaces of the dummy gates, such as by a planarization process,such as a CMP. The CMP may also remove the masks (and, in someinstances, upper portions of the gate spacers 26) on the dummy gates.Accordingly, top surfaces of the dummy gates are exposed through thefirst ILD 32 and the CESL 30. With the dummy gates exposed through thefirst ILD 32 and the CESL 30, the dummy gates are removed, such as byone or more acceptable etch processes. Recesses are formed between gatespacers 26 where the dummy gate stacks are removed, and channel regionsof the fins 22 are exposed through the recesses.

Replacement gate structures 47 are formed in the recesses where thedummy gate stacks were removed. The replacement gate structures 47 (notspecifically numbered in FIG. 3C) each include, as illustrated, aninterfacial dielectric 40, a gate dielectric layer 42, one or moreoptional conformal layers 44, and a gate conductive fill material 46.The interfacial dielectric 40, the gate dielectric layer 42, the one ormore optional conformal layers 44, and the gate conductive fill material46 can be deposited by any appropriate deposition technique. Theinterfacial dielectric 40 is formed on sidewalls and top surfaces of thefins 22 along the channel regions. The interfacial dielectric 40 can be,for example, the interfacial dielectric of the dummy gate stack if notremoved, an oxide (e.g., silicon oxide), a nitride (e.g., siliconnitride), and/or another dielectric layer. The interfacial dielectric40, or a subsequently deposited dielectric layer, is along sidewall andtop surfaces of the fins 22 and on top surfaces of the isolationstructures 24.

The gate dielectric layer 42 can be conformally deposited in therecesses where dummy gate stacks were removed (e.g., on sidewall and topsurfaces of the fins 22, on sidewalls of the gate spacers 26, and on topsurfaces of the isolation structures 24) and on the top surfaces of thefirst ILD 32, the CESL 30, and gate spacers 26. The gate dielectriclayer 42 can be or include silicon oxide, silicon nitride, a high-kdielectric material, multilayers thereof, or other dielectric material.A high-k dielectric material may include a metal oxide of or a metalsilicate of hafnium (Hf), aluminum (Al), zirconium (Zr), lanthanum (La),magnesium (Mg), barium (Ba), titanium (Ti), lead (Pb), or a combinationthereof.

Then, the one or more optional conformal layers 44 can be conformally(and sequentially, if more than one) deposited on the gate dielectriclayer 42. The one or more optional conformal layers 44 can include oneor more barrier and/or capping layers and one or more work-functiontuning layers. The one or more barrier and/or capping layers can includea nitride, silicon nitride, carbon nitride, and/or aluminum nitride oftantalum and/or titanium; a nitride, carbon nitride, and/or carbide oftungsten; the like; or a combination thereof. The one or morework-function tuning layers may include or be a nitride, siliconnitride, carbon nitride, aluminum nitride, aluminum oxide, and/oraluminum carbide of titanium and/or tantalum; a nitride, carbon nitride,and/or carbide of tungsten; cobalt; platinum; the like; or a combinationthereof.

The gate conductive fill material 46 is formed over the one or moreoptional conformal layers 44, if implemented, and/or the gate dielectriclayer 42. The gate conductive fill material 46 can fill remainingrecesses where the dummy gate stacks were removed. The gate conductivefill material 46 may be or comprise a metal-containing material such astungsten, cobalt, aluminum, ruthenium, copper, multi-layers thereof, acombination thereof, or the like. A planarization process, such as aCMP, may remove excess gate conductive fill material 46, one or moreoptional conformal layers 44, and gate dielectric layer 42. Thereplacement gate structures 47 comprising the gate conductive fillmaterial 46, one or more optional conformal layers 44, gate dielectriclayer 42, and interfacial dielectric 40 may therefore be formed asillustrated in FIG. 3C.

A second ILD 48 is formed over the first ILD 32, CESL 30, gate spacers26, and replacement gate structures 47. The second ILD 48 may compriseor be silicon dioxide, a low-k dielectric material, silicon oxynitride,PSG, BSG, BPSG, USG, FSG, OSG, SiO_(x)C_(y), silicon carbon material, acompound thereof, a composite thereof, the like, or a combinationthereof. The second ILD 48 may be deposited by any appropriatedeposition process.

The tri-layer mask is formed over the second ILD 48. The tri-layer maskincludes a first sub-layer 50, a second sub-layer 52, and a thirdsub-layer 54. The first sub-layer 50 is formed over the second ILD 48.The second sub-layer 52 is formed over the first sub-layer 50. The thirdsub-layer 54 is formed over the second sub-layer 52. The first sub-layer50, second sub-layer 52, and third sub-layer 54 are or include differentmaterials from each other so as to provide etch selectivity when etchingthe tri-layer mask. Any appropriate materials may be implemented for thefirst sub-layer 50, second sub-layer 52, and third sub-layer 54. In somespecific examples, the first sub-layer 50 is or includes ametal-containing material, such as a metal nitride (e.g., titaniumnitride (TiN)) or metal carbide (e.g., tungsten carbide (WC)); thesecond sub-layer 52 is or includes an oxide (e.g., silicon oxide(SiO_(x))); and the third sub-layer 54 is or includes silicon (e.g.,amorphous silicon or polysilicon). The first sub-layer 50, secondsub-layer 52, and third sub-layer 54 can be deposited by any appropriatedeposition process, such as chemical vapor deposition (CVD), physicalvapor deposition (PVD), spin-on coating, or the like. In some examples,a thickness of the first sub-layer 50 is in a range from about 15 nm toabout 40 nm; a thickness of the second sub-layer 52 is in a range fromabout 20 nm to about 60 nm; and a thickness of the third sub-layer 54 isin a range from about 20 nm to about 50 nm.

FIGS. 4A, 4B, and 4C illustrate the formation of cut portions 54 c fromthe third sub-layer 54 of the tri-layer mask. The cut portions 54 c, aswill become apparent subsequently, are formed at locations thatintersect trenches that are to be implemented in subsequentphotolithography processes. By intersecting these trenches, the cutportions 54 c will substantially define lateral boundaries of openings(e.g., boundaries that intersect a cross-section parallel to thecross-section X-X) that are to be formed to various components of theFinFET structures. The cut portions 54 c can be formed using appropriatephotolithography and etch processes. The etch process can be ananisotropic etch, such as a reactive ion etch (RIE), an inductivelycoupled plasma (ICP) etch, or another etch process, that selectivelyetches the third sub-layer 54 without significantly etching the secondsub-layer 52.

FIGS. 5A-5C through 8A-8C illustrate double patterning using alithography-etch-lithography-etch (LELE) process. The double patterningcan permit spacing between contacts, such as along the cross-sectionY-Y, to be smaller than lithography limits that a single lithographyprocess may otherwise permit. The order of the lithography-etchprocesses can be altered from what is described herein. As describedherein, a first lithography-etch process is performed with respect toFIGS. 5A-5C and 6A-6C, and a second, subsequent lithography-etch processis performed with respect to FIGS. 7A-7C and 8A-8C. In other examples,the lithography-etch process of FIGS. 7A-7C and 8A-8C is performedbefore the lithography-etch process of FIGS. 5A-5C and 6A-6C. In otherexamples, single patterning processes may be implemented, or otherdouble patterning processes (or more patterning) may be implemented.

FIGS. 5A, 5B, and 5C illustrate the formation of a photoresist 60 withtrenches 62 and the subsequent etching of the second sub-layer 52through the trenches 62. The photoresist 60 can be formed on the cutportions 54 c and the second sub-layer 52, such as by using spin-oncoating, and patterned to have the trenches 62 by exposing thephotoresist 60 to light using an appropriate photomask. Exposed orunexposed portions of the photoresist 60 may then be removed dependingon whether a positive or negative resist is used. Each of the trenches62 can extend across multiple SRAM cells. Each of the trenches 62 canhave a substantially uniform width 62 w across individual and multipleSRAM cells. The trenches 62 in the photoresist 60 are defined by aphotomask that is used in the lithography process that patterns thephotoresist 60, and hence, an exposure pattern of the photomask haspatterns that correspond to the substantially uniform width 62 w of thetrenches 62 in the photoresist 60. The width 62 w of the trenches 62will substantially define lateral boundaries of openings (e.g.,boundaries that intersect a cross-section parallel to the cross-sectionY-Y) that are to be formed to various components of the FinFETstructures. The width 62 w of the trenches 62, in some examples, is in arange from about 8 nm to about 20 nm.

The second sub-layer 52 that is exposed through the trenches 62 isetched. The etch process can be an anisotropic etch, such as a RIE, anICP etch, or another etch process, that selectively etches the secondsub-layer 52 without significantly etching the cut portions 54 c or thefirst sub-layer 50. Hence, as illustrated in FIG. 5A, the cut portions54 c act as a mask for the portions of the second sub-layer 52 on whichthe cut portions 54 c are disposed. As a result, after the etch process,cut portions 54 c and the first sub-layer 50 are exposed through thetrenches 62 of the photoresist 60.

FIGS. 6A, 6B, and 6C illustrate the removal of the photoresist 60. Thephotoresist 60 can be removed by an ashing or wet strip processes, forexample. As a result of the lithography and etch processes of FIGS.5A-5C, openings are formed through the second sub-layer 52 to expose thefirst sub-layer 50. The openings through the second sub-layer 52 formedin FIGS. 5A-5C have lateral lengths that are defined by the cut portions54 c and respective widths corresponding to the width 62 w of thetrenches 62.

FIGS. 7A, 7B, and 7C illustrate the formation of a photoresist 64 withtrenches 66 and the subsequent etching of the second sub-layer 52through the trenches 66. The photoresist 64 can be formed on the cutportions 54 c, the second sub-layer 52, and first sub-layer 50, such asby using spin-on coating, and patterned to have the trenches 66 byexposing the photoresist 64 to light using an appropriate photomask.Exposed or unexposed portions of the photoresist 64 may then be removeddepending on whether a positive or negative resist is used. Each oftrenches 66 of the photoresist 64 can be disposed between whererespective neighboring pairs of the trenches 62 of the photoresist 60where formed as described above with respect to FIGS. 5A-5C. Each of thetrenches 66 can extend across multiple SRAM cells.

Each of the trenches 66 can have a varying width depending upon thelocation of the width in individual and/or multiple SRAM cells. Thetrenches 66 in the photoresist 64 are defined by a photomask that isused in the lithography process that patterns the photoresist 64, andhence, an exposure pattern of the photomask has patterns that correspondto the varying width of the trenches 66 in the photoresist 64. Asillustrated in FIG. 7A, the trenches 66 have a first width 66 w 1 and asecond width 66 w 2. The second width 66 w 2 is greater than the firstwidth 66 w 1. The first width 66 w 1 of the trenches 66 can be equal tothe width 62 w of the trenches 62 formed with respect to FIG. 5A. Thesecond width 66 w 2 is at a location along each trench 66 where aconductive feature having a small lateral length (e.g., in or parallelto the cross section X-X) is to be formed, and the first width 66 w 1 isalong a remainder of the respective trench 66. In some examples, theconductive feature(s) has the smallest lateral length of the conductivefeatures to be formed contacting the FinFET structures of the respectiveSRAM cell. In some examples, the conductive feature(s) that is to beformed based on the second width 66 w 2 of the trench 66 is a bit lineor complementary bit line contact. The width of the trenches 66 willsubstantially define lateral boundaries of openings (e.g., boundariesthat intersect a cross-section parallel to the cross-section Y-Y) thatare to be formed to various components of the FinFET structures. Thefirst width 66 w 1 of the trenches 66, in some examples, is in a rangefrom about 10 nm to about 15 nm, and the second width 66 w 2 is in arange from about 10.5 nm to about 17 nm. The second width 66 w 2 can begreater than the first width 66 w 1 by, for example, at least about 0.5nm, such as about 0.5 nm to about 2 nm.

The second sub-layer 52 that is exposed through the trenches 66 isetched. The etch process can be an anisotropic etch, such as a RIE oranother etch process, that selectively etches the second sub-layer 52without significantly etching the cut portions 54 c or the firstsub-layer 50. Hence, as illustrated in FIG. 7A, the cut portions 54 cact as a mask for the portions of the second sub-layer 52 on which thecut portions 54 c are disposed. As a result, after the etch process, cutportions 54 c and the first sub-layer 50 are exposed through thetrenches 66 of the photoresist 64.

FIGS. 8A, 8B, and 8C illustrate the removal of the photoresist 64. Thephotoresist 64 can be removed by an ashing or wet strip processes, forexample. As a result of the lithography and etch processes of FIGS.7A-7C, openings are formed through the second sub-layer 52 to expose thefirst sub-layer 50. The openings through the second sub-layer 52 formedin FIGS. 7A-7C have lateral lengths that are defined by the cut portions54 c and respective widths corresponding to the first width 66 w 1 andsecond width 66 w 2 of the trenches 66.

FIGS. 9A, 9B, and 9C illustrate transferring the pattern of the secondsub-layer 52 to the first sub-layer 50. The pattern of the secondsub-layer 52 can be transferred to the first sub-layer 50 by an etchprocess. The etch process can be an anisotropic etch, such as a RIE, anICP etch, or another etch process. The etch process can selectively etchthe first sub-layer 50. Although FIGS. 9A, 9B, and 9C illustrate the cutportions 54 c and the exposed portions of the second sub-layer 52partially consumed, the cut portions 54 c and the second sub-layer 52can be removed by and/or remain through the transferring of the patternand through some subsequent processing before being removed. In someexamples, the transferring of the pattern can consume some or all of thecut portions 54 c and the second sub-layer 52, and/or a wet cleanprocess (e.g., ammonium hydroxide (NH₄OH) and/or diluted hydrofluoricacid (dHF)) can remove the cut portions 54 c (e.g., if the cut portions54 c are silicon) and the second sub-layer 52 (e.g., if the secondsub-layer 52 is silicon oxide) after the transfer of the pattern to thefirst sub-layer 50. Transferring the pattern to the first sub-layer 50forms openings through the first sub-layer 50, corresponding to theopenings through the second sub-layer 52, that expose the underlyingsecond ILD 48.

FIGS. 10A, 10B, and 10C illustrate the formation of conductive features(generically, conductive features 70) to respective epitaxialsource/drain structures 28. Using the patterned first sub-layer 50 as amask, openings are etched through the second ILD 48, first ILD 32, andCESL 30 to expose respective epitaxial source/drain structures 28. Theopenings can be formed by using an etch process, such as atomic layeretch (ALE), RIE, ICP etch, or another etch process. After the formationof the openings, conductive features 70 are formed in the openings tothe epitaxial source/drain structures 28. The conductive features 70 mayinclude a silicide region 72 formed on the epitaxial source/drainstructures 28, an adhesion and/or barrier layer 74, and a conductivefill material 76 on the adhesion and/or barrier layer 74, as illustratedin FIGS. 10B and 10C. The silicide region 72 may be formed by thermallyreacting an upper portion of the epitaxial source/drain structures 28with a metal layer (not shown), such as titanium, tantalum, or the like,formed on the epitaxial source/drain structures 28. The adhesion and/orbarrier layer 74 is conformally deposited in the openings. The adhesionand/or barrier layer 74 may be or include titanium nitride, titaniumoxide, tantalum nitride, tantalum oxide, any suitable transition metalnitrides or oxides, the like, or any combination thereof, and may bedeposited by any suitable deposition technique. The conductive fill 76material may be or include cobalt, tungsten, copper, ruthenium,aluminum, gold, silver, alloys thereof, the like, or a combinationthereof, and may be deposited by any suitable deposition technique.After the conductive material 76 is deposited, excess conductive fillmaterial 76, adhesion and/or barrier layer 74, and any remainingtri-layer mask may be removed by using a planarization process, such asa CMP. The conductive features 70 may be referred to as contacts, plugs,etc.

More specifically, first power node conductive features 70VDD, secondpower node conductive features 70VSS, bit line conductive features 70BL,complementary bit line conductive features 70BLB, first intra-cellconductive features 70 nN1, and second intra-cell conductive features 70nN2 are formed. A person having ordinary skill in the art will readilyunderstand the correspondence of these conductive features 70 with theSRAM cells 100 a-d in the layout of FIG. 2. The bit line conductivefeatures 70BL and complementary bit line conductive features 70BLB havea width 70 w 2 and a length 70 l 1. Other conductive features 70 have awidth 70 w 1. As an example, the first power node conductive features70VDD have a length 70 l 2.

The width 70 w 1 corresponds to the widths 62 w and 66 w 1 of thetrenches 62 and 66, respectively. The widths 70 w 2 of the conductivefeatures 70BL and 70BLB correspond to the second width 66 w 2 of thetrenches 66. As a result, the widths 70 w 2 of the conductive features70BL and 70BLB are greater than the widths 70 w 1 of other conductivefeatures 70. In some examples, the width 70 w 2 of each of theconductive features 70BL and 70BLB is in a range from about 15.5 nm toabout 22 nm, and the width 70 w 1 of each of the other conductivefeatures 70 is in a range from about 15 nm to about 20 nm. The width 70w 2 can be greater than the width 70 w 1 by about 0.5 nm or more, suchas by an amount in a range from about 0.5 nm to about 2 nm.

The lengths of the conductive features 70 correspond to the respectivespacing between neighboring cut portions 54 c disposed along respectivetrenches 62 and 66. The lengths of the conductive features 70 can vary.The lengths 70 l 1 of the conductive features 70BL and 70BLB are lessthan the lengths of other conductive features 70 (e.g., such as thelength 70 l 2 of the first power node conductive features 70VDD). Insome examples, the length 70 l 1 of the conductive features 70BL and70BLB is in a range from about 30 nm to about 60 nm. The length 70 l 2of the conductive features 70VDD can be in a range from about 70 nm toabout 100 nm. The length of the conductive features 70N1 and 70N2 can bein a range from about 90 nm to about 120 nm. The length of theconductive features 70VSS can be in a range from about 110 nm to about140 nm. The length 70 l 1 of each of the conductive features 70BL and70BLB can be less than the lengths of each of the other conductivefeatures 70 by an amount in a range from about 20 nm to about 90 nm.

FIGS. 11A-11C through 16A-16C illustrate views of respectiveintermediate structures at respective stages during another exampleprocess for forming an SRAM structure in accordance with someembodiments. The process proceeds as described above with respect toFIGS. 3A-3C through 6A-6C. The process then proceeds to FIGS. 11A-11C asdescribed below.

Similar to above, the process including FIGS. 5A-5C through 6A-6C and11A-11C through 12A-12C illustrate double patterning using alithography-etch-lithography-etch (LELE) process. The order of thelithography-etch processes can be altered from what is described herein.As described herein, a first lithography-etch process is performed withrespect to FIGS. 5A-5C and 6A-6C, and a second, subsequentlithography-etch process is performed with respect to FIGS. 11A-11C and12A-12C. In other examples, the lithography-etch process of FIGS.11A-11C and 12A-12C is performed before the lithography-etch process ofFIGS. 5A-5C and 6A-6C. In other examples, single patterning processesmay be implemented, or other double patterning processes (or morepatterning) may be implemented.

Various etch processes are described in the following processing. Anopening-widening etch process is described as being performed after adescribed etch process below to provide an example. In other examples,various other etch processes implemented to form the opening (such asetch processes that pattern the tri-layer mask and that etch through thesecond ILD 48 and first ILD 32) may implement an opening-widening etchprocess. In other examples, the opening-widening etch process may beperformed between any of the various etch processes and/or in the placeof an anisotropic etch process that is one of the various etchprocesses. Further details will be described below.

FIGS. 11A, 11B, and 11C illustrate the formation of a photoresist 80with trenches 82 and the subsequent etching of the second sub-layer 52through the trenches 82. The photoresist 80 can be formed on the cutportions 54 c, the second sub-layer 52, and first sub-layer 50, such asby using spin-on coating, and patterned to have the trenches 82 byexposing the photoresist 80 to light using an appropriate photomask.Exposed or unexposed portions of the photoresist 80 may then be removeddepending on whether a positive or negative resist is used. Each oftrenches 82 of the photoresist 80 can be disposed between whererespective neighboring pairs of the trenches 82 of the photoresist 60where formed as described above with respect to FIGS. 5A-5C. Each of thetrenches 82 can extend across multiple SRAM cells. Each of the trenches82 can have a substantially uniform width 82 w across individual andmultiple SRAM cells. The trenches 82 in the photoresist 80 are definedby a photomask that is used in the lithography process that patterns thephotoresist 80, and hence, an exposure pattern of the photomask haspatterns that correspond to the substantially uniform width 82 w of thetrenches 82 in the photoresist 80. The width 82 w of the trenches 82will substantially define lateral boundaries of at least some of theopenings (e.g., boundaries that intersect a cross-section parallel tothe cross-section Y-Y) that are to be formed to various components ofthe FinFET structures. The width 82 w of the trenches 82 can be equal tothe width 62 w of the trenches 62 formed with respect to FIG. 5A. Awidth 82 w of the trenches 82, in some examples, is in a range fromabout 40 nm to about 60 nm.

The second sub-layer 52 that is exposed through the trenches 82 isetched. The etch process can be an anisotropic etch, such as a RIE, anICP etch, or another etch process, that selectively etches the secondsub-layer 52 without significantly etching the cut portions 54 c or thefirst sub-layer 50. Hence, as illustrated in FIG. 11A, the cut portions54 c act as a mask for the portions of the second sub-layer 52 on whichthe cut portions 54 c are disposed. As a result, after the etch process,cut portions 54 c and the first sub-layer 50 are exposed through thetrenches 82 of the photoresist 80.

FIGS. 12A, 12B, and 12C illustrate the removal of the photoresist 80.The photoresist 80 can be removed by an ashing or wet strip processes,for example. As a result of the lithography and etch processes of FIGS.11A-11C, openings are formed through the second sub-layer 52 to exposethe first sub-layer 50. The openings through the second sub-layer 52formed in FIGS. 11A-11C have lateral lengths that are defined by the cutportions 54 c and widths corresponding to the width 82 w of the trenches82.

FIGS. 13A, 13B, and 13C illustrate transferring the pattern of thesecond sub-layer 52 to the first sub-layer 50. The pattern of the secondsub-layer 52 can be transferred to the first sub-layer 50 by an etchprocess. The etch process can be an anisotropic etch, such as a RIE, anICP etch, or another etch process. The etch process can selectively etchthe first sub-layer 50. Although FIGS. 13A, 13B, and 13C illustrate thecut portions 54 c and the exposed portions of the second sub-layer 52partially consumed, the cut portions 54 c and the second sub-layer 52can be removed by and/or remain through the transferring of the patternand through some subsequent processing before being removed. In someexamples, the transferring of the pattern can consume some or all of thecut portions 54 c and the second sub-layer 52, and/or a wet cleanprocess can remove the cut portions 54 c and the second sub-layer 52after the transfer of the pattern to the first sub-layer 50.Transferring the pattern to the first sub-layer 50 forms openingsthrough the first sub-layer 50, corresponding to the openings throughthe second sub-layer 52, that expose the underlying second ILD 48.

FIGS. 14A, 14B, and 14C illustrate the formation of openings 86 throughthe second ILD 48 and first ILD 32. In the illustrated example, theopenings 86 are formed to the CESL 30, but in other examples, theopenings 86 may expose the epitaxial source/drain structures 28 or be tovarious other depths in the first ILD 32. The openings 86 can be formedby using an etch process, such as ALE, RIE, ICP etch, or another etchprocess. As illustrated, some of the cut portions 54 c are partiallyconsumed and exposed portions of the second sub-layer 52 are removed bythe etch process, although other examples may consume or remove theseportions differently. The openings 86 have a width 86 w corresponding tothe widths 62 w and 82 w of the trenches 62 and 82, respectively. One ofthe openings 86 is at a location where a conductive feature having asmall lateral length (e.g., in or parallel to the cross section X-X) isto be formed, and that opening 86 has a length 86 l. In some examples,the conductive feature(s) has the smallest lateral length of theconductive features to be formed contacting the FinFET structures of therespective SRAM cell. In some examples, the conductive feature(s) thatis to be formed based on the length 86 l is a bit line or complementarybit line contact.

FIGS. 15A, 15B, and 15C illustrate the widening of the openings at thelocations where conductive features having a small lateral length are tobe formed. The openings 86 at those locations are widened to openings88. The remainder of openings 86 may or may not be significantly widenedand are referred to as openings 90.

The openings 88 are widened by an opening-widening etch process. Theopening-widening etch process can leverage characteristics of theloading effect to widen smaller openings while not significantlywidening larger openings. In some examples, the opening-widening etchprocess includes an etchant gas and a polymer-passivating gas, and aratio of the etchant gas to the polymer-passivating gas is tuned toimplement the opening-widening etch process. In some examples, asubstrate bias and/or a plasma generator source can be pulsed during anetch process to implement the opening-widening etch process. In someexamples, the ratio of gases and pulsing can be implemented.

In some examples, the ratio of the etchant gas to thepolymer-passivating gas is tuned. An inductively coupled plasma reactiveion etching (ICP-RIE) process may be implemented. The ICP-RIE can use acarbon-poor fluorine-based etchant gas (such as CF₄, NF₃, etc.) oranother etchant gas, and can use a carbon-rich polymer-passivating gas(such as CHF₃, CH₂F₂, CH₃F, C₄F₆, C₄F₈, etc.) or another polymer gas. Aflow rate of the etchant gas can be in a range from about 100 sccm toabout 500 sccm, and a flow rate of the polymer-passivating gas can be ina range from about 5 sccm to about 50 sccm. In some examples, a ratio ofthe flow rate of the etchant gas to the flow rate of thepolymer-passivating gas is in a range from about 2 to about 100. Apressure of the ICP-RIE can be in a range from about 10 mTorr to about100 mTorr. A temperature of the ICP-RIE can be in a range from about 40°C. to about 150° C. The plasma generator of the ICP-RIE can be at apower in a range from about 100 W to about 1,000 W, and the substrateholder can be biased to a voltage in a range from about 50 V to about900 V.

In these examples, the ratio of the flow rates is tuned to permit moreetching in smaller openings than in larger openings. A reactant (e.g.,cation and/or radical) from the polymer-passivating gas can diffuse lessinto smaller openings than in larger openings, which can result in lesspassivation in the smaller openings than in the larger openings.Similarly, a reactant (e.g., cation and/or radical) from the etchant gascan diffuse less into smaller openings than in larger openings, whichcan result in less etching of the smaller openings than the largeropenings. The effects of these reactants can be tuned by tuning theratio of the flow rates of the gases such that the smaller openings canhave more lateral etching than the larger openings. Even though lessreactants from the etchant gas can diffuse into a smaller opening than alarger opening, the etch rate in the smaller opening can be greater thanin the larger opening because more reactants from thepolymer-passivating gas can diffuse into the larger opening (andtherefore block the reactants from the etchant gas from etching theunderlying material) than the smaller opening. Various gases and ratioscan be implemented based on the materials being etched as well as thesizes of the various openings.

In some examples, the substrate bias and/or a plasma generator source ispulsed. An ICP-RIE process may be implemented. The ICP-RIE can use afluorine-based etchant gas (such as CF₄, NF₃, etc.) or another etchantgas. A flow rate of the etchant gas can be in a range from about 100sccm to about 500 sccm, and can use a passivating gas (such as CHF₃,CH₂F₂, CH₃F, C₄F₆, C₄F₈, etc.). A pressure of the ICP-RIE can be in arange from about 10 mTorr to about 100 mTorr. A temperature of theICP-RIE can be in a range from about 40° C. to about 150° C. The plasmagenerator of the ICP-RIE can be at a power in a range from about 100 Wto about 1,000 W, and the substrate holder can be biased to a voltage ina range from about 50 V to about 900 V. The power of the plasmagenerator and the bias voltage of the substrate holder can be pulsedsuch that when one is pulsed on (or high) the other is off (or low). Thebias voltage of the substrate holder can be pulsed with a square wavepulse with a duty cycle in a range from about 10% to about 90% and at afrequency in a range from about 10 Hz to about 10 kHz. The power of theplasma generator can also be pulsed with a square wave pulse with a dutycycle in a range from about 10% to about 90% and at a frequency in arange from about 10 Hz to about 10 kHz. The pulsed plasma generator andpulsed bias voltage of the substrate can be synchronous ornon-synchronous.

In these examples, pulsing is tuned to permit more etching in smalleropenings than in larger openings. Referring to FIG. 17, pulsing function102 illustrates an example pulsing of the power of the plasma generator,and pulsing function 104 illustrates an example pulsing of the biasvoltage of the substrate holder. During a first time period 112 when thepower of the plasma generator is pulsed high and the bias voltage of thesubstrate holder is low, etching substantially does not occur, and etchby-product dissociation occurs. During a second time period 114 when thebias voltage of the substrate holder is pulsed high and the power of theplasma generator is low, ions are accelerated causing etching to occur,and etch by-product dissociation does not occur. When the bias voltageof the substrate holder is pulsed on, the process is etch dominated, andwhen the bias voltage of the substrate is low, the process ispassivation dominated. During the periods when the bias voltage is low(e.g., off), more passivation may occur in the large openings than inthe smaller openings. During periods when the bias voltage is pulsed on(and/or when the power of the plasma generator is low), greater etchingoccurs in the larger openings than in the smaller openings. The effectsof these reactants can be tuned by tuning the pulse of the plasmagenerator and/or bias voltage of the substrate to achieve a ratiotherebetween that can have more lateral etching in smaller openings thanin the larger openings.

In some examples, aspects of tuning a ratio of the gases and pulsing canbe implemented. In an example, an ICP-RIE is implemented. The ICP-RIEcan use a carbon-poor fluorine-based etchant gas (such as CF₄, NF₃,etc.) or another etchant gas, and can use a carbon-richpolymer-passivating gas (such as CHF₃, CH₂F₂, CH₃F, C₄F₆, C₄F₈, etc.) oranother polymer gas. A flow rate of the etchant gas can be in a rangefrom about 100 sccm to about 500 sccm, and a flow rate of thepolymer-passivating gas can be in a range from about 5 sccm to about 50sccm. In some examples, a ratio of the flow rate of the etchant gas tothe flow rate of the polymer-passivating gas is in a range from about 2to about 100. A pressure of the ICP-RIE can be in a range from about 10mTorr to about 100 mTorr. A temperature of the ICP-RIE can be in a rangefrom about 40° C. to about 150° C. The plasma generator of the ICP-RIEcan be at a power in a range from about 100 W to about 1,000 W, and thesubstrate holder can be biased to a voltage in a range from about 50 Vto about 900 V. The power of the plasma generator and the bias voltageof the substrate holder can be pulsed such that when one is pulsed on(or high) the other is off (or low). The bias voltage of the substrateholder can be pulsed with a square wave pulse with a duty cycle in arange from about 10% to about 90% and at a frequency in a range fromabout 10 Hz to about 10 kHz. The power of the plasma generator can alsobe pulsed with a square wave pulse with a duty cycle in a range fromabout 10% to about 90% and at a frequency in a range from about 10 Hz toabout 10 kHz. The pulsed plasma generator and pulsed bias voltage of thesubstrate can be synchronous or non-synchronous.

FIGS. 15A, 15B, and 15C further illustrate a width 88 w and a length 88l of the opening 88 that is widened by the opening-widening etchprocess. In some examples, the width 88 w can be in a range from about15 nm to about 25 nm, and the length 88 l can be in a range from about30 nm to about 60 nm. The width 88 w can be an increase from the width86 w by an amount in a range from about 0.5 nm to about 2 nm, and thelength 88 l can be an increase from the length 86 l by an amount in arange from about 0.5 nm to about 3 nm.

As indicated previously, the opening-widening etch process may beperformed at different instances during processing. In some examples,the opening-widening etch process may be performed as the etch processthat patterns the second sub-layer 52 in FIGS. 11A-11C, or after theetch process that patterns the second sub-layer 52 in FIGS. 11A-11C butbefore the etch process that patterns the first sub-layer 50 in FIGS.13A-13C. In some examples, the opening-widening etch process may beperformed as the etch process that patterns the first sub-layer 50 inFIGS. 13A-13C, or after the etch process that patterns the firstsub-layer 50 in FIGS. 13A-13C but before the etch process that forms theopenings 86 in FIGS. 14A-14C. In some examples, the opening-wideningetch process may be performed as the etch process that forms theopenings 86 in FIGS. 14A-14C. Various combinations or permutations ofthese etch processes may be implemented.

FIGS. 16A, 16B, and 16C illustrate the formation of conductive features(generically, conductive features 92) to respective epitaxialsource/drain structures 28. Conductive features 92 are formed in theopenings 88 and 90 to the epitaxial source/drain structures 28. Theconductive features 92 may include a silicide region 94 formed on theepitaxial source/drain structures 28, an adhesion and/or barrier layer96, and a conductive fill material 98 on the adhesion and/or barrierlayer 96. The conductive features 92 can be formed with the same orsimilar materials and by the same or similar processed as describedabove with respect to FIGS. 10A-10C. The conductive features 92 may bereferred to as contacts, plugs, etc.

More specifically, first power node conductive features 92VDD, secondpower node conductive features 92VSS, bit line conductive features 92BL,complementary bit line conductive features 92BLB, first intra-cellconductive features 92 nN1, and second intra-cell conductive features 92nN2 are formed. A person having ordinary skill in the art will readilyunderstand the correspondence of these conductive features 92 with theSRAM cells 100 a-d in the layout of FIG. 2. The bit line conductivefeatures 92BL and complementary bit line conductive features 92BLB havea width 92 w 2 and a length 92 l 1. Other conductive features 92 have awidth 92 w 1. As an example, the first power node conductive features92VDD have a length 92 l 2.

The width 92 w 1 corresponds to the widths 86 w of the openings 86. Thewidths 92 w 2 of the conductive features 92BL and 92BLB correspond tothe width 88 w of the openings 88. As a result, the widths 92 w 2 of theconductive features 92BL and 92BLB are greater than the widths 92 w 1 ofother conductive features 92. In some examples, the width 92 w 2 of eachof the conductive features 92BL and 92BLB is in a range from about 15 nmto about 25 nm, and the width 92 w 1 of each of the other conductivefeatures 92 is in a range from about 14.5 nm to about 22 nm. The width92 w 2 can be greater than the width 92 w 1 by an amount in a range fromabout 0.5 nm to about 3 nm.

The lengths of the conductive features 92 substantially correspond tothe respective spacing between neighboring cut portions 54 c disposedalong respective trenches 62 and 82. The lengths of the conductivefeatures 92 can vary. The lengths 92 l 1 of the conductive features 92BLand 92BLB can be enlarged from the spacing between respective cutportions 54 c and are less than the lengths of other conductive features92 (e.g., such as the length 92 l 2 of the first power node conductivefeatures 92VDD). In some examples, the length 92 l 1 of each of theconductive features 92BL and 92BLB is in a range from about 30 nm toabout 60 nm. The length 92 l 1 of each of the conductive features 92BLand 92BLB can be less than the lengths of each of the other conductivefeatures 92 by an amount in a range from about 20 nm to about 90 nm.

As described previously, some examples can form wider bit line andcomplementary bit line conductive features by tuning a lithographyprocess, and some examples can form wider bit line and complementary bitline conductive features by tuning an etch process. In other examples,various aspects of these preceding examples can be combined to achievewider conductive features, such as wider bit line and complementary bitline conductive features.

Embodiments described herein can achieve advantages. By having anincreased width of openings that have small lengths, gap fill of theconductive fill material in the openings may be improved. With improvedgap fill, the conductive fill material of conductive features (that areformed in the openings with the increased widths and small lengths) canbe void free. For example, the bit line conductive features andcomplementary bit line conductive features in the SRAM layouts describedherein may be void free. Further, by increasing the widths of thesmaller openings, the widths of larger openings (with larger lengths)can be decreased. By decreasing the widths of the larger openings, adistance between the openings (and hence, the conductive features formedin those openings) can be increased, which increases a processing windowand reduces a risk of overlay with gate structures due to misalignment.Various other advantages may be achieved.

An embodiment is a structure. The structure includes a substrate, adielectric layer over the substrate, a first conductive feature throughthe dielectric layer to a first source/drain region on the substrate,and a second conductive feature through the dielectric layer to a secondsource/drain region on the substrate. The first conductive feature has afirst length along a longitudinal axis of the first conductive featureand a first width perpendicular to the first length. The secondconductive feature has a second length along a longitudinal axis of thesecond conductive feature and a second width perpendicular to the secondlength. The longitudinal axis of the first conductive feature is alignedwith the longitudinal axis of the second conductive feature. The firstwidth is greater than the second width, and the first length is lessthan the second length.

Another embodiment is a structure. The structure includes a substrate, astatic random access memory (SRAM) structure on the substrate, adielectric layer over the SRAM structure on the substrate, a bit linecontact through the dielectric layer to the SRAM structure, and a firstpower node contact through the dielectric layer to the SRAM structure. Alength of the first power node contact is aligned with a length of thebit line contact. The length of the first power node contact is greaterthan the length of the bit line contact, and a width of the first powernode contact is less than a width of the bit line contact.

A further embodiment is a method. A dielectric layer is deposited on asubstrate. A mask is deposited over the dielectric layer. A photoresistis patterned over the mask. The photoresist has a trench. A first maskopening and a second mask opening are etched through the mask. Etchingthe first mask opening and the second mask opening includes etching themask through the trench in the photoresist. A first contact opening anda second contact opening are etched through the dielectric layer.Etching the first contact opening and the second contact openingincludes etching the dielectric layer through the first mask opening toform the first contact opening and etching the dielectric layer throughthe second mask opening to form the second contact opening. The firstcontact opening and second contact opening have respective lengths thatare aligned and correspond to a length of the trench in the photoresist.A width of the first contact opening is greater than a width of thesecond contact opening. The first contact opening and the second contactopening are filled with a conductive material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming a semiconductor device, themethod comprising: forming a first insulating layer over a firstconductive feature and a second conductive feature: forming a first masklayer over the first insulating layer forming a second mask layer overthe first mask layer: forming a third mask layer over the second masklayer; patterning the third mask layer to form a first feature; forminga fourth mask layer over the second mask layer and the first feature;patterning the fourth mask layer to form a first trench in the fourthmask layer, wherein at least a portion of the first feature is exposedin the first trench; etching the second mask layer to form a secondtrench in the second mask layer under the first trench using the fourthmask layer and the first feature as a mask; etching the first mask layerto form a third trench in the first mask layer under the second trench,a first portion of the third trench being on a first side of the firstfeature and a second portion of the third trench being on a second sideof the first feature in a plan view; and widening a width of the thirdtrench, wherein the second portion is widened more than the firstportion.
 2. The method of claim 1, wherein the first portion of thethird trench is larger than the second portion of the third trench. 3.The method of claim 1, wherein the widening comprises an etch processusing an etchant gas and a polymer-passivating gas.
 4. The method ofclaim 1, wherein the widening comprises an inductively coupled plasmareactive ion etching (ICP-RIE) process.
 5. The method of claim 4,wherein the ICP-RIE uses a carbon-poor fluorine-based etchant gas. 6.The method of claim 5, wherein the carbon-poor fluorine-based etchantgas comprises CF₄ or NF₃.
 7. The method of claim 5, wherein the ICP-RIEuses a carbon-rich polymer-passivating gas.
 8. The method of claim 7,wherein the carbon-rich polymer-passivating gas comprises CHF₃, CH₂F₂,CH₃F, C₄F₆, or C₄F₈.
 9. The method of claim 7, wherein a flow rate ofthe carbon-poor fluorine-based etchant gas is in a range between 100sccm and 500 sccm, wherein a flow rate of the carbon-richpolymer-passivating gas is in a range between 5 sccm and 50 sccm.
 10. Amethod of forming a semiconductor device, the method comprising: forminga first insulating layer over a first conductive feature and a secondconductive feature: forming a first mask layer over the first insulatinglayer; forming a second mask layer over the first mask layer: patterningthe second mask layer to form a first feature; patterning the first masklayer to form a trench, wherein a first portion of the trench is on afirst side of the first feature and a second portion of the trench is ona second side of the first feature in a plan view; extending the firstportion and the second portion of the trench into the first insulatinglayer; widening the trench, wherein the second portion of the trench iswidened more than the first portion; and filling the first portion andthe second portion of the trench with a conductive material.
 11. Themethod of claim 10, wherein patterning the second mask layer forms asecond feature and a third feature, wherein after patterning the firstmask layer to form the trench, the first portion of the trench extendsfrom the first feature to the second feature, wherein the second portionof the trench extends from the first feature to the third feature,wherein a length of the first portion of the trench is greater than alength of the second portion of the trench.
 12. The method of claim 10,wherein the conductive material in the second portion is a bit line of amemory cell.
 13. The method of claim 10, wherein the second portion ison a first cell boundary of a memory structure.
 14. The method of claim13, wherein the second portion is on a second cell boundary of thememory structure.
 15. The method of claim 10, wherein the conductivematerial in the second portion is a first source/drain contact, andwherein the conductive material in the first portion is a secondsource/drain contact.
 16. The method of claim 15, wherein a gatestructure is between the first source/drain contact and the secondsource/drain contact.
 17. A method of forming a semiconductor device,the method comprising: forming a first insulating layer over a firstconductive feature and a second conductive feature: forming a patternedmask over the first insulating layer patterning the first insulatinglayer to form a first trench over the first conductive feature and asecond trench over the second conductive feature; performing a wideningprocess, wherein the widening process widens the second trench iswidened more than the first trench; after performing the wideningprocess, removing the patterned mask; and filling the first trench andthe second trench with a conductive material.
 18. The method of claim17, wherein filling the first trench and the second trench forms a firstsource/drain contact of a transistor and a second source/drain contactof the transistor, respectively.
 19. The method of claim 17, whereinafter performing the widening process, the second trench is 0.5 nm to 3nm wider than the first trench.
 20. The method of claim 17, wherein atleast a portion of the first insulating layer extends under theconductive material in the second trench, wherein a first edge of thesecond trench is directly over the second conductive feature.